One of the most difficult problems in the field of corrosion inhibition is that of preventing and/or inhibiting corrosion in oxygenated aqueous systems, such as in water floods, cooling towers, drilling muds, air drilling, auto radiator systems, etc. Many corrosion inhibitors capable of performing in non-aqueous systems and/or non-oxygenated systems perform poorly in aqueous and/or oxygenated systems (i.e. aerobic systems).
Pyrophosphates are one non-limiting example of a type of corrosion inhibitor used as corrosion inhibitors in oxygenated systems. Ethoxylated fatty alcohol may react with phosphorous pentasulfide to form O,O-disubstituted dithiophosphoric acid and pyrophosphates as described in U.S. Pat. No. 4,075,291, which is herein incorporated by reference in its entirety. The '291 patent sets forth the following reactions for obtaining the pyrophosphate products:

The O,O-disubstituted dithiophosphoric acid initially formed may proceed through an anhydride formation and/or an isomerization to yield the pyrophosphates as shown in the above reactions. The final reaction yields about 40% O,O-disubstituted dithiophosphoric acid as a final product and 60% pyrophosphates and anhydride products. Even though much of the hydrogen sulfide is removed from the initial reaction products, hydrogen sulfide may still form from the anhydride formation and/or isomerization of the O,O-disubstituted dithiophosphoric acid reaction, even after storage and handling of the resulting product. Thus, hydrogen sulfide may be released into the environment upon usage of the pyrophosphates.
After removing hydrogen sulfide from the initial reaction, hydrogen sulfide may be produced form the labile P—S—H linkage in the O,O-disubstituted dithiophosphoric acid. The water formed from the pyrophosphate reaction and/or moisture in the storage container, under normal handling conditions, may react with O,O-disubstituted dithiophosphoric acid to form additional hydrogen sulfide. This additional hydrogen sulfide tends to accumulate in the headspace of a storage container and has been difficult to remove prior to using the product (e.g. pyrophosphates). Since water will react with O,O-disubstituted dithiophosphoric acid and pyrophosphates to release more H2S, any mitigation efforts should involve non-aqueous additives. As such, traditional H2S scavengers like triazines containing water cannot be used for this application.
It would be desirable if alternative corrosion inhibitors were devised that do not react with other components within a current system and/or are less toxic to the environment and less corrosive.